陈列图在靠墙货架上放置在（）的空隙。
A.左边
B.右边
C.上边
D.下边
参考答案：A
For many years we have been keeping in ____by sending each other e-mails or phone calls.
A．connection
B．contrast
C．relation
D．touch
液流水头损失分为沿程水头损失和局部水头损失。（）
